This invention is generally directed to toner and developer compositions, and more specifically the present invention is directed to toner compositions, including magnetic, single component, two component and colored toner compositions, and imaging processes thereof, wherein at least one polymeric resin and a charge additive compound, including at least one wax component, can be selected such that the toner and developer compositions have enhanced development properties and improved copy quality performance for extended periods over the life time of the developer composition. In one embodiment of the present invention, toner compositions containing at least two polymers, and in other embodiments, from about 2 to about 10 polymers comprised of, for example, one or more resins and optional crosslinked resin, a wax component, and a charge control agent retention additive (CCARA) component are selected for use in the imaging processes. In another embodiment of the present invention, the toner compositions are comprised of resin particles, comprised especially a first resin and a second crosslinked resin, pigment particles, a wax component, such as polypropylene wax, and a copolymer CCARA, such as a block copolymer, or a graft copolymer. There is also provided in accordance with the present invention positively charged toner compositions comprised of resin particles, pigment particles, a wax component, such as polypropylene wax, and a copolymer charge control agent retention additive, such as a block copolymer, or a graft copolymer, and charge enhancing additives. In addition, the present invention is directed to developer compositions comprised of the aforementioned toners, and carrier particles. Furthermore, in another embodiment of the present invention there are provided single component toner compositions comprised of resin particles, magnetic components, such as magnetites, a wax component, such as polypropylene wax, and a copolymer charge control agent retention additive or compound, such as a block copolymer, or a graft copolymer, The toner and developer compositions of the present invention are useful in a number of known electrostatographic imaging and printing systems, especially those systems wherein a charge control agent and/or a wax is present in the toner. The developer compositions of the present invention, in embodiments, possess a wide fusing latitude, for example about 100.degree. C., which is the temperature range between the minimum fixing temperature of, for example, from about 100.degree. C. to about 170.degree. C. required for fixing toner particles on paper and the hot, for example, from about 180.degree. C. to about 250.degree. C., offset temperature. The developer compositions of the present invention also provide toner images with low surface energy and a low frictional coefficient, which properties enable the effective release of paper from the fuser roll and provide for a reduction in image smudging. Further, the developer compositions and imaging processes of the present invention possess stable electrical properties for extended time periods, and with these compositions, for example, there is no substantial change in the triboelectrical charging values. The toner tribo product stabilizes quickly and maintains a high and constant level over many thousands of imaging cycles.
The following patents are of interest to the background of the present invention, the disclosures of which are incorporated by reference herein in their entirety:
U.S. Pat. No. 5,229,242, to Mahabadi, et al., discloses the use of a synthetic rubber, KRATON G1726X, commercially available from Shell Chemical. The compound is believed to act as a scavenger for free wax within the toner formulation. The synthetic rubber apparently reduces free wax domains that may be created during melt mixing. The synthetic rubber it is believed codissolves the wax component with the toner resin component or alternatively compatibilizes the wax and toner resin phases so that the wax content cannot become free or phase separated during micronization of the toner or in the product toner particles resulting therefrom. This reference also discloses other references which teach toner compositions containing resin particles and polyalkylene compounds such as polyethylene and polypropylene of molecular weight of about 1,500 to about 20,000. These polyalkylene compounds are believed to prevent offsetting in electrostatic imaging processes as disclosed in col. 2, lines 15 to 20 of the reference.
Other patents of interest include: U.S. Pat. No. 4,795,689 which discloses an electrostatic image developing toner comprising as essential constituents a nonlinear polymer, a low melting polymer, which is incompatible with the nonlinear polymer, a copolymer composed of a segmented polymer which is at least compatible with the nonlinear polymer, and a segmented polymer which is at least compatible with the low melting polymer, and a coloring agent, see the Abstract, and columns 3 to 10 for example; U.S. Pat. No. 4,557,991 which discloses a toner for the development of electrostatic images comprised of a certain binder resin, and a wax comprising a polyolefin, see the Abstract; also see columns 5 and 6 of this patent and note the disclosure that the modified component shows an affinity to the binder and is high in compatibility with the binder, column 6, line 25; and as collateral interest see U S. Pat. No. 3,965,021.
Developer and toner compositions with certain waxes therein, which waxes can be selected as a component for the toners of the present invention, are known. For example, there are illustrated in U.K. Patent Publication 1,442,835, toner compositions containing resin particles, and polyalkylene compounds, such as polyethylene and polypropylene of a molecular weight of from about 1,500 to about 20,000, reference page 3, lines 97 to 119, which compositions prevent toner offsetting in electrostatic imaging processes. Additionally, the '835 publication discloses the addition of paraffin waxes together with, or without a metal salt of a fatty acid, reference page 2, lines 55 to 58. Also, in U.S. Pat. No. 4,997,739, there is illustrated a toner formulation including polypropylene wax (MW: from about 200 to about 6,000) to improve hot offset. In addition, many patents disclose the use of metal salts of fatty acids for incorporation into toner compositions, such as U.S. Pat. No. 3,655,374. Also, it is known that the aforementioned toner compositions with metal salts of fatty acids can be selected for electrostatic imaging methods wherein blade cleaning of the photoreceptor is accomplished, reference U.S. Pat. No. 3,635,704. Additionally, there are illustrated in U.S. Pat. No. 3,983,045 three component developer compositions comprising toner particles, a friction reducing material, and a finely divided non smearable abrasive material, reference column 4, beginning at line 31. Examples of friction reducing materials include saturated or unsaturated, substituted or unsubstituted, fatty acids preferably of from 8 to 35 carbon atoms, or metal salts of such fatty acids; fatty alcohols corresponding to said acids; mono and polyhydric alcohol esters of said acids and corresponding amides; polyethylene glycols and methoxy-polyethylene glycols; terephthalic acids; and the like, reference column 7, lines 13 to 43.
Described in U.S. Pat. No. 4,367,275 are methods of preventing offsetting of electrostatic images of the toner composition to the fuser roll, which toner subsequently offsets to supporting substrates such as papers wherein there is selected toner compositions containing specific external lubricants including various waxes, see column 5, lines 32 to 45.
However, there are various problems observed with the inclusion of polyolefin or other waxes, or wax-like additives, in toner formulations. For example, when a polypropylene wax is included in toner to enhance the release of toner from a hot fuser roll, or to improve the lubrication of fixed toner image it has been observed that the wax does not typically disperse well in the toner resin. As a result, free wax particles are released during the pulverizing step in, for example, a fluid energy mill and the pulverization rate is lower. The poor dispersion of wax in the toner resin and, therefore, the loss of wax will then impair the release function it is designed for. Scratch marks, for example, on xerographic developed toner solid areas caused by stripper fingers are observed as a result of poor release. Furthermore, the free wax remaining in the developer will build up on the detone roll present in the xerographic apparatus causing a hardware failure.
The toner formulations, in embodiments of the present invention, are comprised of resin particles, pigment particles, surface additives, for example, flow aids or lubricant release agents, and one or more charge control agent retention additives or compounds. Certain surface additives such as lubricants, and waxes in particular, do not have the above mentioned problem with phase separation from the toner formulations of the present invention as demonstrated by photomicrographic analysis of micronized toners. The wax domain size of toners formulations prepared in the present invention are approximately constant in size of from about 0.5 to about 2.0 micrometers in diameter. The wax domain size is not readily influenced by the presence of a charge control retention agent or synthetic rubber additive. However, the triboelectric properties of toner formulations of the present invention which do not contain a charge control agent retention additive are conspicuously short lived and are of little value in high volume or high speed xerographic printing processes.
All the problems mentioned above, and others can be eliminated, or minimized with the toner compositions and processes of the present invention in embodiments thereof. The release of wax particles is, for example, a result of poor wax dispersion during the toner mechanical blending step. All internal charge control additives should be dispersed well in the primary toner resin for them to impart their specific functions to the toner and thus the developer. Some of the charge control agent additives, such as quaternary ammonium salts, may become a separate molten phase during melt mixing or may transfer to the carrier surface during contact charging with the carrier particles. Some degree of success has been obtained by mechanical blending the toner formulation in certain types of mixers, such as the known Banbury mixer, where the temperature of melt can be maintained at a low level and polymer viscosities are not that far apart. However, it has been found difficult to generate an effective dispersions of certain charge control agents in compounding extruders where melt temperatures are typically higher.
The inclusion of a charge control agent retention additive or compound of the present invention is designed to overcome the inherent incompatibilities between different polymeric resins, between toner resin and wax, and more specifically, between the toner resin or resins and the charge control additive or between the wax and the charge control additive, thus widening the processing temperature latitude and enabling toner preparation in a large variety of equipment types, for example an extruder. The improvement in thermodynamic compatibility of the charge additive and other toner components also provides for a more stable dispersion of internally dispersed charge control additive compounds, such as quaternary ammonium salts, in the host resin which dispersion is stabilized against gross phase separation over time. Although not desired to be limited by theory, it is believed that the inhibition of phase separation of the charge control additive from other toner components, such as the resin component, by the charge control agent retention additive or compound, provides a mechanism for enhanced developer longevity and thereby stabilizes the developer tribo product characteristics and developer image quality.
A number of specific advantages are associated with the invention of the present application in embodiments thereof, including improving the dispersion of toner resin particles, especially a mixture of resins and wax; improving the dispersion of wax in the toner, thus eliminating the undesirable release of wax from the toner in the form of free wax particles during the pulverizing operation of the toner manufacturing process and the subsequent contamination of xerographic machine subsystems by these free wax particles; improving the dispersion of certain charge control additives in the toner resin or resins; avoiding the pulverizing rate reduction resulting from the poor wax dispersion; maintaining the intended concentration of wax in the toner to provide enhancement during release from the fuser roll and avoiding the undesirable scratch marks caused by the stripper fingers; a wide process latitude can be provided during the mechanical blending operation of the toner manufacturing process; enabling the effective mechanical blending of toner to be accomplished in a number of devices, including an extruder; and providing toner compositions with extended developer tribo product life time and xerographic development processes with improved stability and performance, and enhanced image quality.